Process for the preparation of organic acids



Patented Dec.26,1933

. 1,940,987 I raocii ss FOR THE PREPARATION or ORGANIC ACIDS p i John C. woodhouse, Wilmington, Del., assignor to E. I. du;Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. 'Application April 23, 1931 Serial No. 532,275'

Claims. (o1. 260-116) Thisfinvention relates to a process forthe forproducts is high, I havefound that their formamation of organic compounds and particularly tion can be inhibited and, some cases, sub- 'to the preparation of moncoarboxylic acids by stantially eliminated by employing a process the. interaction of aliphatic alcohols and carbon utilizing recirculation;the 'acid formed being 6 monoxide'in thepresen'c e of a catalyst. removed from the system. i 60 It is known that organic acids and esters can By this'process, it is possible to carry out the be prepared by the interaction, in the'vapor or Synthesis of organic acids, such as acetic acid, liquid phase, of organic compounds with theoxp pion acid, i acid, from e e t ides of carbon. For example, it has been shown '10Wer hOi Of the s in Conjunction Wi h 10 that the condensation of methyl alcohol with carbon monoxide, more efficientlye h e there s 65 carbon monoxide, in the presence of a suitable larger proportion of the raw materials converted catalyst, will produce acetic acid and meth l into the acid, and arelatively smaller amount acetate in proportions governed by the particular of lily-Products to be p fied' operating conditions. "Acids have likewise been As stated v ;v s r th r hy r r n formed from methane and carbon dioxide, from a d b n s a e generally termed together '10 carbon monoxide and water, and from ethersand w h the acetic acid duringxthe y i f he carbon monoxide. latter. Similar by-products, of course, are In the actual operation of the above processes d wh n the higher acids being p it is difiicult, if not impossible, to so controlthe repa d: In t actual p t n of y invention,

1- action that no compound, other than the orh i s pr fe a to ov r m t 5 ganic acid sought, is produced. For instance, ca s g. from e r n only t a dwhe ynth izi ti a id by th passage f formed and to recirculate to the reaction zone the carbon monoxideand methanol over a catalyst, t -pr ucts. and unconverted g JQt O S there may be formed in conjunction with the of s t p a u u y op as s; to

25 acetic acid, dimethyl ether, methyl iormate, and 900 m h r s end-fi d these Conditions 1,80

perhaps some a methyl acetate s with generally bf'the Products other h n h permanent gases,

some carbon dioxide and methane. Consequent t h m i G, h dr n, qu d at ly, the costoi producingthe acid is greatly inp ra u es: In separatin the or-' V creased over aprocess involving no byproductf 8401a; therefore, f o e gaseous mixture formation furthe vt byproducts of fractional condensation may be utilized to efiect5 the reaction, While of some value, are undesirable e' removal of subs ntially all the acid and as theynot only lower the yield oithe acidproe fremihe mixture Other means a e duced but also require larger equipment cost for employedto rea i e this result althou h fracsame output f acidtional condensation under elevated or atmos- An object of the present invention is to prolphelidpressure is W611 p f this P IDO vide a process for. the preparation of organic uslibseiquentite t removahof the id acids in which the formation of by-products is W r, the e h gaseous mixture is rcuinhibited. Another object ofthe invention is leted, again through the o e s o Chamberaftto provide-a process for the recirculation of the ad to it the necessary aw materials.

* 40 by-products formed during the reaction in or- S c methane and'otherfinert ga such ascarder to suppress their further formation. A still vD011"dioxide, may e e i ooneentrationin the further object of the invention is toprovide a] 'circu1atine.. ea it is saryi D process for the preparation of organic acids in i y continuously W thdraw from the cirwhich the organic acid in the gaseous products il y y t 'an appropriate amo j,' h 45 is fractionally condensed therefrom, and the residual gases, preferably after separation of the other compounds presentrecirculated through .acid f r l t e /or the process. I, V ,carbon dioxide maybe kept downrto a limiting Z Other objects and advantages of the invenconcentration. Bysuitably adjusting the amount hon will be apparentas it is better understood f f is s s0w t w nd r ulating the pro- 1 50 by reference to the following spec'ificationin portions of alcohol and carbon monoxide added which its detailsandpreierred embodiments are to the reaction, the Iimitingproportion of these described. 7 I- r inerts to the reactants can readily be maintained. ,In carrying out gaseous reactions forthe prep-' Upon, starting up a circulatoryprocess of this aration of organicgacids from alcohols and car-p type it will usually be foundthat the concentrabon monoxide inpwhich the formation of bytionfof the inert gases increasescontinuoufly; As llO V a result the partial pressure of the reactants decreases and a lower yield of the acid is eventually obtained. It is of advantage, therefore, to bleed off a portion of the gaseous mixture at a point between the fractional condensation step and the point at which the gaseous mixture is reintroduced into the reaction chamber. The bled-off gases are subjected to a scrubbing and/or fractional condensation operation which separates the mixture into two fractions: one fraction containing compounds which react with carbon monoxide preferably in the presence of water to give acetic acid are returned to the reaction chamber; the other fraction is vented. By this step the concentration of the inert gases, or any other constituent, the concentration of which it may be desired to control, may be maintained.

Although the invention is susceptible of embodiments in many forms which may differ as to conditions of operation as well as to materials and apparatus employed, the following example will serve to illustrate one method of applying the invention to the s'ynthesisof acetic acid and its esters.

The apparatus consists of a compressor, of which the parts contacting with the gases to react are constructed of materials which are not readily attacked by the gases employed, the compressor being adapted to bring the gases to the pressure at which the reaction is eifected,a reaction apparatus in which is disposed a'catalyst suitable for the synthesis of acetic acid, a condenser for fractional condensation, a receiver for collecting the condensed acid of the reaction, a second'condenser for the purging operation, and a regulating pump. The reaction apparatus, condenser, receiver, second condenser, and circulating pump are connected in a series circuit in the order named, with a by-pass around the second condenser, and through this system is circulated continuously a body of agaseous medium, such as carbon monoxide, under a pressure of 700 atmospheres. The catalyst, which may consist, for example, of silico-tungstic acid, is heated initially to reaction temperature by electrical means, and it having attained that temperature, a gaseous mixture containing approximately equal molal' proportions of carbon monoxide, and methanol containing approximately 10% water, if desired, compressed to 700 atmospheres, is gradually admitted to the circulatory system where it is passed at a temperature of approximately 350 C. over L the acetic acid-forming catalyst disposed in the reaction apparatus. The carbon monoxide and methanol combine to form acetic acid and byproducts, the former and water are condensed by fractional condensation in the condenser and collected in the receiver. The greater proportion of the residual gases by-pass the second condenser and are returned by the circulatory pump to the reaction apparatus, where, together with additional proportions of a suitable mixture of meth- "afnol, water, and carbon monoxide, they undergo further reaction to produce the acetic acid. Provision is made, by means of the second fractional condenser, for continuously withdrawing residual gas from the system, stripping therefrom compounds other than methane and carbon monoxide, capable of yielding acetic acid, and returning them to the system. When the reaction is under way,

the quantity of carbon monoxide and methanol added to the system are regulated, at all times, so

' that the carbon monoxide and methanol concentration contacting with the catalyst is substantially uniform.

After the catalyst has been initially heated to reaction temperature, the electrical heating is in part or Wholly dispensed with, as may be required, and the temperature of the reaction may be thereafter controlled for the most part by regulating the concentration of the circulating gas employed.

From a consideration of the above disclosure, it will be realized that various reactants may be catalytically converted into oganic compounds containing a negative radical of an aliphatic acid, and all such reactions will come within the scope of the invention if the formation of the by-products of the reaction be inhibited by the recirculation process as hereinbefore described.

I claim:

1. A process for the synthesis of organic acids which comprises passing carbon monoxide and an aliphatic alcohol into a circulating gaseous medium containing a high concentration of byproducts of the reaction, circulating the resulting gaseous mixture over a heated catalyst adapted for the synthesis, removing the organic acid formed and recirculating the separated byproducts over the catalyst, while maintaining a substantially uniform concentration of the reacting gaseous mixture.

2. A process for the synthesis 'of organic acids which comprises passing carbon monoxide and an aliphatic alcohol into a circulating gaseous medium containing a high concentration of byproducts of the reaction, circulating the resulting gaseous mixture over a heated catalyst adapted for the synthesis, removing the organic acid formed from the circulating gases, while maintaining a high concentration of the byproducts of the reaction in the gases passing over the catalyst.

3. A process for the synthesis of organic acids which comprises passing carbon monoxide and an aliphatic alcohol into a circulating gaseous medium containing a high concentration of byproducts of the reaction, circulating the resulting gaseous mixture over a heated catalyst adapted for the synthesis, removing the organic acid' formed and water from the circulating gases, by a fractional condensation step in which only the acetic acid and water are substantially wholly removed, while maintaining a substantially uniform concentration of the reacting gaseous mix ture.

4. A process for the synthesis of acetic acid which comprises continuously contacting with a heated catalyst a gaseous mixture of carbon monoxide and methanol containing a high concentration of by-products of the reaction, such as dimethyl ether, methyl formats, methane, etc., the acetic acid being substantially completely removed from the gases prior to their recirculation over the catalyst, while maintaining a substan- -13 lyst adapted for said synthesis, removing the acetic acid formed by fractional condensation and recirculating the separated lay-products over the catalyst, while maintaining a I substantially uniform concentration of inert gases during con-'- tact with the catalyst by separation of portions of the circulating mixture and replacement thereof with fresh mixtures of gases for the reaction.

6. In a process for the synthesis of organic acids the step which comprises passingcarbon monoxide and an aliphatic alcohol into acircu lating gaseous medium containing a highconcentration of by-products of the reaction,.circulating the resulting gaseous mixture over a heated" catalyst adapted for the synthesis, removing the organic acid formed from the circulating gases,

stantially uniform concentration of the carbon;

monoxide and methanol by continuous withdrawal of portions of the gaseous mixture immediately subsequent to the removal therefrom,

of the acetic acid. and replacement of that portion of the gaseous mixture removed byrresh carbon monoxide and alcohol.

8. In a vapor phase circulatory process for'the synthesis of organic acids, the method of controlling the relative quantities of acids and byproducts produced, which consists in maintaining .a high co ncentration of all the by-products of the reaction in the circulating gaseous mixtureand removing the organic acid products therefrom, while maintaining a substantially uniform concentration of' the reacting gases contained therein, by continuous withdrawal of portions and replacement thereof with the reactants. 9. In a vapor phase circulatory process for the preparation of aliphatic monocarboxylic acids by the interaction of aliphatic monohydroxy alcohols with carbon monoxide, the method of controlling the relative quantities of acid and byproducts produced, which consists in maintaining a high concentration of all the by-products of the reaction in the circulatory gaseous mixture, and removing the organic acids therefrom,

while maintaining 'a substantially uniform concentration of the reacting gases contained therein, by continuous withdrawal of portions and replacement thereof by fresh carbon'monoxide and alcohols.

10. In a vapor phase circulatory process for the synthesis'of acetic acid from methanol and carbon monoxide the method of controlling the relative quantities of acetic acid and by-products produced which consists in maintaining a high a concentration of all the by-products of the reaction in the circulatory gaseous mixture, and

removing the acetic acid therefrom while mainta ining a substantially uniform concentration of carbon monoxide and methanol, by continuous withdrawal of portions and replacement thereof with carbon monoxide and methanol.

' JOHN C. WOODHOUSE. 

